The following discussion of the prior art is provided to place the invention in an appropriate technical context and enable the advantages of it to be more fully understood. It should be appreciated, however, that any discussion of the prior art throughout the specification should not be considered as an express or implied admission that such prior art is widely known or forms part of common general knowledge in the field.
A polyamide is one of the polymers which are frequently used as engineering plastics for a very wide range of applications. A polyamide molding composition is of significant commercial interest and may be used to produce automobile or electrical components, generally by injection molding, in view of weight reduction, ease in assembling parts/components and also its design flexibility.
For particular applications, such as automobile engine components including radiator end tank, air intake manifold, water pump body, intercooler air duct, timing belt cover, electrical connector and engine cover, which are to be exposed to high temperature during their lifecycle, required is a polyamide molding composition which is capable of exhibiting excellent mechanical strength and thermal stability, i.e., high performance retention of mechanical properties such as tensile strength (TS) to break and Charpy impact strength after thermal aging, good spiral flow, and minimum distortion during injection molding as well as low moisture content and excellent salt crack resistance.
In general, a polyamide molding composition comprising reinforcing fillers exhibits excellent mechanical properties such as impact strength, flexural properties, and excellent toughness in addition to good heat resistance, and thus can be substituted for metal materials, which have been used as structural materials for automobiles. Normally, those structural materials are used in chemically aggressive environments, e.g., antifreeze at elevated temperatures and deicing agent commonly used on the roads during winter time.
Polyamide 6,6 is frequently used when high mechanical strength and good stability under heat is required, but polyamide 6,6 is also susceptible to hydrolysis, and exhibits relatively low resistance to chlorides, e.g., sodium chloride, calcium chloride, and zinc chloride, which are particularly useful to prevent ice formation and to deice the surface of roads by depressing the freezing point of water, and also exhibits low resistance to ethylene glycol and propylene glycol, which are commonly used as antifreeze in an engine cooling system.
Further, ionic lubricants, such as metal soaps, e.g., Al salts, Zn salts, alkali metal salts, alkaline earth metal salts, or esters or amides of fatty acids, in particular the soaps of alkaline earth metals are widely used to stabilize plastics, functioning as release agents in polyamides and polyesters, as stabilizers in PVC, and also as acid acceptors in polyolefins. Metal soaps are commonly incorporated into a polyamide composition as lubricant to prevent a polyamide molding composition from adhering to the surface of a mold, and also used as nucleating agents in polyamides. Some lubricants also contribute to reducing melt viscosity of a polyamide composition and thus increasing flowability thereof. In addition, the presence of ionic lubricants within a polyamide composition reinforced with fillers such as glass fibers is normally detrimental to the impact strength of the polyamide composition, since ionic lubricants tend to hinder the binding of glass fibers to polyamides.
It is hence required a polyamide 6,6 composition, which comprises at least one reinforcing filler and at least one ionic lubricant, exhibiting good resistance to chemicals and having melt viscosity appropriate for injection molding, while maintaining advantageous mechanical and thermal properties thereof. For instance, PCT publication No. WO 2013/041594 A1 (Rhodia Operations) discloses a blend of a polyamide 6,6, of which the amount of amine end group (AEG) is greater than the amount of carboxylic acid end group (CEG), with a polyamide 6,10, which may remedy the drawbacks of a polyamide 6,6 composition as above mentioned, but no mention is made regarding the presence of an ionic lubricant and its effect on the melt viscosity of a polyamide composition.
Therefore, a polyamide 6,6 composition, which comprises at least one reinforcing filler and at least one ionic lubricant, exhibiting flowability appropriate for injection molding in addition to other advantageous properties as above mentioned, is required in this technology field. The high chain-length polyamide, such as polyamide 6,10 is particularly advantageous in the present invention in view of its mechanical strength, gas barrier property, particularly against refrigerants, high temperature properties, and/or environmental friendliness.